CVE-2026-90359
UnknownSummary
In the Linux kernel, btf_distill_func_proto() builds the function model used for fentry/fexit/fmod_ret/fsession trampolines and struct_ops, having accepted a 16-byte __int128 return value since the trampoline was introduced. However, the BPF trampoline preserves only 8 bytes of the return value (RAX/R0), so for attach types that read the target's return value (fexit, fmod_ret, fsession plus their _multi variants, and struct_ops) the second half is neither saved nor restored, corrupting the value seen by the real caller.
Risk Assessment
Return value corruption can lead to incorrect BPF program behavior and unpredictable kernel behavior, potentially with security consequences.
Recommendation
Update the Linux kernel to a version containing the fix that rejects >8 byte return values in bpf_check_attach_target(), bpf_check_attach_btf_id_multi(), and bpf_struct_ops_desc_init().
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: bpf: Reject >8 byte return values on return-reading trampoline paths btf_distill_func_proto() builds the function model used for the fentry/fexit/fmod_ret/fsession trampolines and struct_ops. It has accepted a 16-byte __int128 return value since the trampoline was introduced: __get_type_size() returns the integer's type size, and the return-type check only rejected ret < 0. But the BPF trampoline preserves only 8 bytes of the return value (RAX on x86, i.e. R0). For an attach type that reads the target's return value the second half (RDX / R3) is neither saved nor restored, so a program attached to a function returning a 16-byte value corrupts the value seen by the real caller and itself observes only half of it. struct_ops trampolines have the same limitation. This affects the attach types that read the target's return value: fexit, fmod_ret and fsession (plus the _multi variants of fexit and fsession), and struct_ops. fentry/fentry_multi run before the target returns and are unaffected. Reject a >8 byte return value for these attach types in bpf_check_attach_target() and bpf_check_attach_btf_id_multi(), and for struct_ops in bpf_struct_ops_desc_init().
Vulnerability data from NVD (NIST) · CISA KEV · EPSS